It is well known that many oil and gas wells require stimulation in order to increase production either as part of well completion, or as part of well work-over. Well stimulation involves the pumping of proppants and fluids under high pressure into the annulus of the well in order to break up subterranean formations and release hydrocarbons into the wellbore, where they can be extracted to the surface. Since it is generally not economically feasible to manufacture wellhead equipment that can withstand extreme pressures, the wellhead must be isolated or removed during well stimulation in order to prevent potential damage and/or injury.
In is well known that it is advantageous to stimulate certain wells, especially gas wells through a production tubing of the well. This permits the well to be stimulated without removing the production tubing from the well, which saves considerable time and reduces service fees.
It is well known that these well stimulation procedures can be performed by connecting a well stimulation tool mandrel to a top of a tubing hanger that supports the production tubing in the well. Before the well stimulation tool mandrel can be connected to the top of the tubing hanger, natural pressure in the well must be contained to prevent the escape of hydrocarbons to atmosphere. Well pressure containment is accomplished in one of two well known ways. First, the well may be “killed” by pumping an overbearing fluid into the well. Killing the well is, however, generally not desirable for a number of reasons. First, the operation is generally expensive and second, the production zones may be plugged or damaged by the overbearing fluid. A second method more commonly used is to seal the production tubing prior to removing a wellhead control stack. The production tubing is sealed using a wireline lubricator to insert a wireline plug into the production tubing string below the tubing hanger. Once the tubing is sealed, the wellhead control stack can be removed from the well and the well stimulation tool can be mounted directly or indirectly to the top of a tubing head spool that supports the tubing hanger. The well stimulation tool mandrel is then screwed into box threads in a top end of an axial passage through the tubing hanger, in a manner well known in the art.
After the well stimulation tool is mounted to the tubing hanger, the wireline plug in the production tubing must be removed to permit the well stimulation procedure to commence. Consequently, the wireline lubricator is used to run in the wireline and retrieve the wireline plug. Thereafter, high pressure lines are connected to the well stimulation tool and high pressure fluids are pumped into the well to acidize or fracture the hydrocarbon producing zones(s).
After the well has been stimulated and the stimulation fluids flowed back out of the well, the production tubing must be sealed again to permit the well stimulation tool to be removed from the tubing head spool. Consequently, the wireline unit must be brought back to the job site, and the wireline lubricator mounted to the top of the well stimulation tool. The wireline is run in to set the wireline plug in the production tubing string. The well stimulation tool can then be safely removed and the wellhead control stack re-mounted to the tubing head spool. After the wellhead control stack is remounted to the tubing head spool, the wireline must be run in again to retrieve the plug before the production of hydrocarbon can be recommenced.
As is well understood by those skilled in the art, wireline services are expensive and time consuming.
There therefore exists a need for a simpler and more economical method and apparatus for stimulating wells using a well stimulation tool mandrel connected to a top of the tubing hanger in a live well.